Dave Chicoine's books are pretty thorough in their describing the various maladies of Old West firearms.
For a new spring - contact Wolff Springs.
Yeah, they provide 'short-stroke' and other C&WAS 'competition' springs, but the point is - they make springs, and they make them for a 'very' wide range of firearms.
Call them and tell them what you need - you should be pleased with their reply.
Vaya,
Scouts Out!